JPS595595A - Thin film el element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention utilizes the application of an alternating current electric field to generate E L (Elect
r.

The present invention relates to the structure of a thin film EL element that emits light (luminescence), and is intended to particularly improve external light emitting efficiency.

Conventionally, AC-operated thin film EL devices have been used with 0, 1-2.0 to improve dielectric strength, luminous efficiency, operational stability, etc.
A three-layer structure in which a semiconductor light-emitting layer such as ZnSJZnSe doped with wt% Mn (or CunAl!, Br, etc.) is mixed with a dielectric material such as Y2O3, TiO2, etc. ZnS:Mn (
Alternatively, a Zn5e:Mn) EL device has been developed, and it has been confirmed whether the various light emitting characteristics are improved. This thin film EL element is K
It emits high-intensity light when an alternating current electric field of Hz is applied, and has a long lifespan.

Furthermore, the light emission of this thin film EL element has a hysteresis characteristic in which the luminance of the light emitted by the same applied voltage differs between the process of increasing the applied voltage and the process of decreasing the voltage from the high voltage side. In the process of increasing the applied voltage to the thin film EL element that was discovered and has this hysteresis characteristic, light, electric field, heat, etc. are applied to the thin film EL element.
The L element is excited to a state of luminescence brightness corresponding to its intensity, and even if the light, electric field, heat, etc. are removed and returned to the original state, the luminance remains high, a so-called memory phenomenon. This led to the development of a new field of use for display technology.

FIG. 1 shows the basic structure of a ZnS:Mn thin film EL device as an example of a thin film EL device.

The structure of the thin film EL element will be explained in detail based on FIG. 1.KIn203. Transparent type @2 such as SnO2, and Y2O layered on top of it.

A first dielectric layer 3 made of TiOz, Al2O3, 5i3Na, SiO2, etc. is formed in an overlapping manner by sputtering, electron beam evaporation, or the like. A ZnS light emitting layer 4 is formed on the first dielectric layer 3 by electron beam evaporation of ZnS:Mn sintered pellets. At this time, the ZnS:Mn sintered pellets used for vapor deposition are pellets in which Mn, which is an active substance, is set at a concentration depending on the purpose.

Z, n S On the light emitting layer 4 is a second dielectric layer 5 made of a material selected from the same group of citrus materials as the first dielectric layer 3.
A back electrode 6 made of A4 or the like is further formed by vapor deposition thereon. The transparent electrode 2 and the back electrode 6 are connected to an AC type #7, and the thin film EL element is driven.

When a 2.61 mK AC voltage is applied to the electrodes, the above AC voltage will be induced between the two dielectric layers 5 on both sides of the ZnS light emitting layer 40, and therefore the ZnS light emitting layer 40 will be excited to the conduction band by the electric field generated within the light emitting layer 4. The accelerated electrons that have obtained sufficient energy directly excite the Mn luminescence center, and when the excited Mn luminescence center returns to the ground state, it emits yellow-orange light. In other words, electrons accelerated in a high electric field become Z
nS Excites the electrons of the Mn atoms that have entered the Zn site, which is the luminescent center in the luminescent layer 4, and when they fall to the ground state, exhibits strong luminescence in a wide wavelength range with a peak of approximately 5850A. When a rare earth fluoride other than Mn is used as the active substance, green and other luminescent colors characteristic of this rare earth element can be obtained.

However, in the thin EL device having the above structure, it is impossible to lead all of the output light inside the light emitting layer to the outside. That is, although the light emission in the light emitting layer is isotropic,
Most of this is trapped inside the thin film EL element due to total reflection at the optical interface on the way to the outside.

The refractive index of the transparent electrode, dielectric layer, and light emitting layer is nTE.
*Represented by nrNSLnEM, n E M > n
If T E 5nrNs>1, all photons having an emission angle with respect to the element surface that is a total reflection critical angle of 6 or more are totally reflected and confined within the element. This situation is shown in FIG.

,! -IJ Here, θ is θ: S1n −T, according to Snell's law.

is given by That is, of the light emitted within the light-emitting layer at a solid angle of 4π, only the light at a solid angle of 4z (, 1-cos θ) is extracted to the outside. External luminous intensity B.

is given by the following equation using the internal emission intensity Bi.

For example, if n I M-2,3 (corresponding to ZnS), 90% of the internal light emission will not be led out to the outside and will be confined inside.

In view of the above problems, it is an object of the present invention to establish a structure of a thin film light emitting device in which the formula (1) does not hold, and to provide a new and useful thin film EL device that increases external light emitting efficiency rather than internal light emitting efficiency. It is something.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

FIGS. 3 and 4 are explanatory views of the main part configuration of a thin 1-inch EL element, respectively, explaining one embodiment of the present invention.

As shown in FIG. 3, a transparent electrode 2, a dielectric layer 3°54,
, In at least one layer of the optical layer 4, grain boundaries are formed so as to form a visible light scattering structure, so that the structure does not satisfy equation (1). Figure @3 shows an example in which scattering grain boundaries 8 are formed within the light emitting layer 4. The light generated at the light emitting center in the light emitting layer 4 becomes multidirectional at the scattering grain boundary 8 in the light emitting layer 4, and the light traveling in a direction that is not totally reflected is guided to the outside.

Alternatively, in the process of forming at least one layer of the transparent electrode 2, the dielectric layers 3 and 5, and the light-emitting layer 4, as shown in FIG. 4, the interface is not flat but has an uneven shape that can sufficiently scatter visible light. Therefore, the structure is such that equation (1) does not hold.

Equation (1) does not hold - In the element structure, even light with a radiation angle greater than the critical angle of total reflection 6 is diffusely reflected within the element, producing a component with a radiation angle smaller than the critical angle of total reflection θ, which is reflected externally. taken out.

From the above, the following equation holds true instead of equation (1).

The device according to the invention allows no external light to enter! It also shows so-called white turbidity without scattering for iIJ.

The scattering grain boundaries 8 in the light-emitting layer 4 are formed by partially dividing the vapor deposition material in the vapor deposition process, so that the dividing boundary surface becomes the scattering grain boundary 8.
It is formed by a method such as

Further, irregularities on the bonding interface can be easily formed by polishing, etching, etc.

FIG. 5 is a graph showing applied voltage vs. luminance brightness (B-V) characteristics. Curve 11 in the figure is the element of the above example,
I2 is a conventional element mainly for specular reflection. curve lI
As is clear from the above, the thin EL device of the above example achieved a remarkable increase in luminance.

As described in detail above, according to the present invention, by forming a scattering/reflection structure for output light inside the element, external light emission efficiency can be significantly increased.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the basic structure of a thin 1-millimeter EL element. Figure 2 is an explanatory diagram showing the progress process of output light. Fig. 5 is a diagram showing the main parts of a thin EL element having a thickness of 115 m in one example. Fig. 5 is a characteristic diagram showing applied voltage vs. luminance luminance characteristics. ■... Glass substrate, 2... Transparent electrode, 3.5・
...Dielectric layer, 4...Light emitting layer, 6...Back electrode, 8...Scattering grain boundary. Agent Patent attorney Aihiko Fuku (and 2 others) Figure 4 190 200 210
Pressure 220Gp no Figure 5

Claims (1)

[Claims] 1. In a thin film EL element in which a thin film structure having a light emitting layer that emits EL light upon application of a voltage is interposed between a pair of electrodes, a scattering structure as an output destination is formed in the thin film structure. Thin film EL element with 1#.